What is the primary capability of the "penetrant testing" method in non-destructive examination?

The primary capability of penetrant testing in non-destructive examination is to detect any indication open to the surface. This method involves applying a liquid penetrant to the surface of a material. If there are discontinuities such as cracks, porosity, or laps that are open to the surface, the penetrant seeps into these flaws. After a specified dwell time, excess penetrant is removed, and a developer is applied, which draws out the penetrant from the flaws, making them visible for inspection. This makes penetrant testing particularly effective for identifying surface-breaking defects in a variety of materials, especially metals.

While there are other methods used for different purposes, penetrant testing is specifically designed for surface indications. It does not detect subsurface defects or anomalies that are beneath the surface of the material, which is where other techniques like ultrasonic testing or magnetic particle testing may be more appropriate. Additionally, it cannot assess the integrity of welds before they are executed, as this method is focused solely on existing surface defects.